Page 31 - JSOM Fall 2025

FIGURE 4
!"#$ &
!"#* !"#$%& Sketches of
*
'
intravenous
ṁ tubing on the
',) ',"
!"#$ & left and thermal
resistor circuit on
!"#$ ) !"#( !"#$%& !"#( $%'"()!$*% !"#$ &
the right.
'
were made across different environmental temperatures. At en- FIGURE 6 Outlet fluid temperature as a function of thermal
vironmental temperatures above 0°C, the outlet fluid tempera- conductivity (insulation thickness is 2.5mm).
ture reaches the ideal 37°C with 2.5mm insulation thickness.
As the environmental temperature decreases to –0.26°C and
–15.3°C, a 7.5mm insulation thickness is required to main-
tain the desired outlet temperature. However, at an extreme
low of –39°C, the outlet fluid temperature fails to reach the
target 37°C even with 25mm-thick insulation. Furthermore,
applying 25mm-thick insulation to the IV tubing results in an
overall outer tubing diameter of 55mm, which is impractical
for emergency medical scenarios due to the time-consuming
nature of its application. These findings suggest that an alter-
native insulating material with superior thermal properties to
polyethylene foam must be identified for extremely low envi-
ronmental temperatures.
FIGURE 5 Effect of insulation thickness on the outlet fluid a clinically appropriate outlet fluid temperature. The subse-
temperature for various environmental temperatures.
quent section of this study explores the influence of varying
IV tubing lengths.

Effect of Tubing Length
The second proposed method for mitigating heat loss in the
IV tubing involves reducing the tubing length. Figure 7 illus-
trates the relationship between outlet fluid temperature, tub-
ing length, and insulation thickness. The range of insulation
thickness values examined is consistent with those presented
in Figure 5. Tubing length varied from 0 to 2m, with the upper
bound representing the length of the existing IV tubing.

For the analysis, the thermal conductivity of the insulation
The mathematical model uses experimental measurements of material is held constant at 0.0432W/(m·K), corresponding to
temperature and flow rate. Because of slight variations in in- polyethylene foam. The multivariable analysis enables the si-
let temperatures between experimental cases, an unexpected multaneous evaluation of the effects of tubing length and insu-
result was observed: the outlet temperature for the 8.4°C am- lation thickness on outlet fluid temperature, providing insights
bient condition exceeded that of the 19.85°C condition. Spe- into potential design optimizations for the IV tubing system.
cifically, the inlet temperature for the 8.4°C ambient case was
40.1°C, while for the 19.85°C case, it was 39.2°C. Figures 7 and 8 demonstrate a significant inverse relationship
between IV tubing length and outlet fluid temperature. The
Figure 6 illustrates the relationship between outlet fluid tem- data suggest that reducing the length of the IV tubing results
perature and insulation material thermal conductivity, ranging in a substantial increase in the outlet fluid temperature. This
from 0 to 0.2W/(m·K), based on experimental data collected finding has important implications for the design of insulated
across a range of environmental temperatures (19.85°C to IV tubing systems. The results indicate that shortening the IV
–39°C). For the analysis, the insulation thickness was main- tubing length may be a crucial factor in developing a practi-
tained at a constant 2.5mm to isolate the effect of material cal and clinically appropriate solution for maintaining fluid
thermal conductivity. temperature during administration. This approach, combined
with optimized insulation properties, could potentially pro-
A significant finding from this analysis is that at an environ- vide a more effective method for preserving fluid temperature
mental temperature of –39°C, no thermal conductivity value within the desired range, particularly in challenging environ-
within the tested range produces an outlet fluid temperature mental conditions.
at or above the target of 37°C. This result suggests that in-
sulation properties alone are insufficient to maintain the de- Conclusion
sired outlet fluid temperature under extreme cold conditions.
Given these findings, it is evident that additional parameters Military personnel operating in cold environments require
beyond insulation characteristics must be considered to achieve FWB transfusion kits capable of delivering blood to patients at

Mitigating FWB Heat Loss During Austere Transfusions | 29